Apparatus for determining the frequency of alternating currents.



Patented 1an. 2|, |902.

'Ala

NNI..

No. 69|,44|,. Y

- H. s. CARR. l Y

APPARATUS FOR DETERMINING THEFBEGUENGYDF ALTERNATING CURRENTS.

(Applicafion ledI July 12, 1901.) A

'i' y A UNiTED STATES' PATENT' OFFICE.

HUGH S.I CARR, OF LAWRENCE, KANSAS.

l APPARATUS FUR DETERMINING THE FREQUENCY OF ALTERNATING CURRENTS.

SPECIFICATION forming part of Letters Patent No. 691,441, dated January21, 1902.

Application filed July 12, 190i.. Serial No. 67,9'83. (No model.)

To all whoml it may concern:

Be it known that I, HUGH S. CARR, a citizen of the United States,residing at Lawrence,

in the county of Douglas and State of Kansas,

5 have invented certain new and usefulV Improvements in Apparatus vforDetermining the Frequency of Alternating Currents, of

which the following is a specification, reference being had vto thedrawings accompanying and forming a part of the same.

The invention, subject of my present application, is a new and improvedapparatus by means of which the frequency of an alternating current maybe accurately and readily determined at any time and by means of whichthe difference of phase in alternatingcurrent devices may beascertained.

The underlying principle of my improved apparatus is that of thestroboscopic effect of a revolving disk divided into alternate sectorswith reiiecting and non-reecting surfaces or composed of alternatetranslucent and opaque materials. I have found that if such a disk berevolved in the light produced by an arc or incandescent lamp which isconnected with an alternating-current circuit the slight iiuctuations inthe intensity of the.

light due to the variations in the strength of the current will producethe illusion of a revolution of the sectors whenever the alternations ofthe current andV the revolutions of the disk are not in synchronism. Ifthe number of revolutions per second of the disk be in excess of thenumber of alternations per second of the current, the apparentrevolutionof the sectors is clockwise when the disk revolves clockwise, While ifthe number of alternations exceeds the number of revolutions per unit oftime the apparent movement of the sectors is counter-clockwise when the'disk revolves clockwise. When, however, the number of revolutions of thedisk and alternations of the current are the same, the sectors Awillappear stationary, andthe same will be true if the number of revolutionsof the disk is any exact multiple of onehalf the number of alternations.

In alternating-current work it isfrequently of considerable practicaland commercial importance to be able to determine at any instant therate of alternation of some given alternating-current generator. Indeterminingalso the efficiencies and working conditions of transformersin nearly all alternatingcurrent devices the frequency of alternationenters directly as an important factor, and its quick and'accurate.determination is essential both for the best conditions of operation andstructural design. It is, moreover, of great importance in the runningof alternating devices in conjunction with each other to determine themoments of synchronism.

The frequency of an alternating current is usually determinedbycalculations based upon the number of poles, the special constructionof the generator, and the speed at which the latter is driven; but sincethis speed is subject to sudden and inevitable changes such calculationsare only approximate and cannot be relied upon as affording accurateinformation as to conditions which may exist at any given instant.Moreover, this means of determining frequencies is not available attransformer-substations orA atl any point remote from the generator, inwhich cases there is no practical means of which I am aware by whicheven approximately accurate calculations of frequency can be made. Incarrying out my invention by utilizing the peculiar effect of analternating-current lamp upon a revolving stroboscopic disk I have useda disk of metal with alternate black and white sectors painted upon it.-This I have revolved by means of a small motor suppliedfrom the samecircuit as the lamp, using a rheostat to regulate the speed of themotor. A suitable tachometer is used for indicating at any instant thespeed of the motor, and when it isbrought to the point where the rays oflight of the lamp reflected from the disk cause the sectors to appearstationary the motor, or the disk, if the latter be directly connectedto the shaft of the motor, Willbe found to be running in synchronismwith the alternating-current generator. If

the disk is running ybelow s ynchronism and right-handed,the sectorswill appear to revolve counter-clockwise, while if running abovesynchronism they will revolve clockwise. If the disk be divided into thesame number of alternate segments as the number of poles in thealternating-current generator, then the speed of the motor and disk willbe the same as that of the generator when the rays of light from thelamp used make the sectors appear stationary. These latter will alsoappear stationary, as has been stated above, when the disk is running athalf speed or one and a half times the speed or twice the speed of thegenerator; but the most stable condition is when the disk is running atthe same speed as the generator.

In practice I have found that transmitted rays are preferable toreliected light, because with the latter an arc-lamp is almostnecessary, and this is not so convenient and available as anincandescent lamp. I therefore employ one or more alternatingincandescent lamps inclosed in a suitable case, one side of which iscomposed of some translucent material, such as tracing-cloth. In frontof these lamps a disk composed of alternate vsolid and opaque andcutaway or translucent sectors is mounted, and when the latter isrevolved a clear and pronounced strobescopic effect is produced,whichmay be easily seen even in daylight, so that the device can be used atany time as Well as at any point on an alternating system. Therevolutions of the disk may be effected in any conven ient manner, as bymotors connected with the alternating circuit itself or from any othersource, and the disk may be either within or without the case.

This apparatus can also be used as a phase indicator for two or morealternating currents in the following manner: The rays of light from thearc or incandescent lamp on one generator-circuit are made to appearstationary by a proper adjustment of the speed of the disk. Then therays of light from a lamp on the second circuit are thrown on the diskand made to coincide with the rays from the first lamp by adjusting thespeed of the second generator or motor. At the instant when the rayscoincide the two machines are in synchronism and capable of beingoperated in conjunction.

My improved apparatus in the preferred form in which I have constructedthe same is illustrated in the accompanying drawings, in Which- Figure lis a front elevation of the device, and Fig. 2 is a sectional plan ofthe same.

The working parts of the instrument are contained within a case F,having a circular opening in front,which is preferably covered by aground-glass plate F or a sheet of translucent material, such astracing-cloth. Within the case there is mounted a motor B, which may beeither an alternating motor, adapted to be run by current from thealternating-current circuit, or a continuous-current motor to be runfrom an independent source.

Any suitable means is employed for regulating and varying the speed ofthis motor, and in illustration of such a device I have shown a variablerheostat E in the circuit thereof.

Connected with the motor and preferably mounted directly upon its shaftis a disk A, composed of alternate sectors of translucent and opaquematerials, and immediately back of said disk, or between the same andthe motor, are placed one or more lamps C, in this case shown asincandescent lamps, the terminals of which are made accessible to enablethem to be connected by wires G with the alternating-current circuit.

The shaft of the motor B is connect-ed With any proper form ofspeed-indicator-as, for example, a small direct current generator withconstant field excitation and a voltmeter connected with thearmature-circuit thereof or any other device, such as an ordinarytachometer. Such a device is indicated by the letter D.

It will now be understood from the above description that this apparatusmay be used at any point in an alternating-current system fordetermining at any instant the frequency of the current, and in thisresides the chief merit and practical value of the device.

Having now described my invention, what I claim is l. An apparatus fordetermining at any instant the frequency of an alternating current,comprising in combination, a stroboscopic disk, a motor for rotating thesame, and means for regulating the speed of the motor, a speedindicatortherefor and one or more lamps adapted to Ibe connected with thealternating current circuit and so located with respect to the diskthatthe fluctuatingillumination will produce a stroboscopic effect, as setforth.

2. An apparatus for determining at any instant the frequency of analternating current, comprising in combination, an electromagneticmotor, a stroboscopic disk mounted directly on the shaft of said motor,one or more electric lamps adapted to be operated by connection with thealternating circuit, and means for Varying and for indicating the speedof the motor, as set forth.

3. An apparatus for determining at any instant the frequency of analternating current, comprising in combination, a box or case, anelectromagnetic motor therein, a disk composed of alternate sectors oftransparent and opaque materials and mounted directly upon themotor-shaft, one or more electric lamps adapted to be operated byconnection With the alternating-current circuit and placed back of thedisk within the case, and means for varying and for indicating the speedof the motor, as set forth.

ft. An apparatus for determining at any instant the frequency of analternating current, comprising in combination an electromagnetic motoradapted to be operated by con- IOO IIO

nectiou'wth the alternating-current circuit, a. disk composed ofalternate sectors of translucent and. opaque materials mounted directlyon the shaft of said motor, one or more electric lamps adaptedto receivecurrent from the alternating current circuit and placed back of saiddisk, a speed-indicator connected with the motor-shaft and means forVarying the speed of the motor, as set forth.

HUGH s. CARR.

Witnesses:

J. F. MALICK, JOHN HUGHES.

